In the production of heat exchangers with plate-like elements, e.g. in the production of so-called plate heat exchangers, a stack of plates can be assembled together and soldered at their points or zones of mutual contact, generally in a furnace, oven or like chamber provided with heating means. The solder can be provided with heating means. The solder can be provided upon the contacting edges or surfaces previously and, when the plates are brought to the soldering temperature, the solder is caused to flow to bond the adjacent plates together.
A furnace for this purpose has been provided heretofore (see, for example, German open application DT-OS No. 22 54 769) and can comprise electrical heating rods or other heating elements disposed in the interior of the furnace through which a protective gas is circulated by a blower. The stack of plates to be soldered together is introduced into the furnace chamber and generally must be preheated so that the soldering temperature can be generated quickly and as uniformly as possible within the chamber. Reference may also be had to U.S. Pat. Nos. 2,293,996, 2,389,175, 2,282,226, 2,944,504, 3,517,916, 3,816,901 and 3,756,489.
This system, wherein the circulating gas only passes around the stack, has been found to have disadvantages and to require considerable work on the part of operating personnel in that, not only must the workpieces be preheated in a separate step, but the preheated pieces must be assembled together and/or the assembled stack subjected to careful preheating.
In spite of these procedures, it has been found that the heating of the plates is not uniform within the chamber and hence certain portions may not reach the soldering temperature while other portions may be overheated. In other words a uniform heat distribution within the workpiece stack at the soldering temperature can be attained only with difficulty in the conventional arrangement.